Advances in electronic technology require a highly regulated voltage supply, regardless of the fluctuation in loads or input power sources. The two fundamental techniques to produce regulated voltage are linear voltage regulator and switching voltage regulator. Linear voltage regulators are typically an amplitude modulation circuit in which the amplitude of the input unregulated voltage is modulated to achieve the constant output voltage. Switching voltage regulators typically employ a duty cycle modulation circuit in which the duty cycle (the percent of the circuit ON time) of the unregulated voltage is modulated.
Linear voltage regulators are simple and cost effective, with quick response and quiet since there is no high-frequency switching noise. The major drawback of linear voltage regulators is the voltage drop in the amplitude modulation circuit, resulting in a loss of power transfer efficiency with high heat dissipation. Switching voltage regulators operate by rapidly turning on and off the input power supply, thus the voltage drop across the duty cycle modulation can be small, resulting in higher power transfer efficiency and less heat dissipation. In return, the design of switching voltage regulators is complex, such as the requirements of high frequency switching circuit and the filtering circuit of the output voltage to achieve low ripple output voltage.
To combine the benefits, some designs use both regulation methods in board level series. For example, a switching voltage regulator may provide the initial regulation and efficiently generate an intermediate voltage slightly above the ultimate output voltage, then this intermediate voltage is further regulated by a linear voltage regulator. This hybrid circuit still suffers from large circuit area, and a somewhat slower response to output voltage disturbances.